나 보다 (appears to be, seems)

This pattern connects an observation to a logical conclusion. You see a friend yawning a lot. You conclude they are tired. You say 피곤한가 봐요. You see a long line at a bakery. You conclude the bread is delicious. You say 빵이 맛있나 봐요. It is all about that external evidence. You cannot use this for your own internal feelings. If you are hungry, you just say 배고파요. You do not say 배고픈가 봐요 about yourself. That would sound like you are watching yourself from outside. Unless you have amnesia, keep it for others! It is like a grammar traffic light. It signals that your statement is based on what is happening around you.

1. 1For present tense verbs, add -나 보다 to the stem. 먹다 becomes 먹나 보다. 가다 becomes 가나 보다.
2. 2For present tense adjectives, add -(으)ㄴ가 보다. 바쁘다 becomes 바쁜가 봐요. 작다 becomes 작은가 봐요.
3. 3For nouns, use 인가 보다. 학생 becomes 학생인가 봐요. 선생님 becomes 선생님인가 봐요.
4. 4For past tense (both verbs and adjectives), use -았/었나 보다. 갔다 becomes 갔나 봐요. 예뻤다 becomes 예뻤나 봐요.
5. 5Note that in casual speech, many Koreans use -나 보다 for adjectives too. However, -(으)ㄴ가 보다 is the technically correct form for adjectives. Using the correct one makes you look like a pro.

Use it when you see a physical sign. Imagine you are at a restaurant. You see a customer sweating and drinking lots of water. You can whisper, "매운가 봐요" (It must be spicy). Use it when you hear something. You hear loud music from your neighbor's house. You can say, "파티를 하나 봐요" (They must be having a party). Use it during a job interview. If the interviewer smiles a lot, tell your friend, "분위기가 좋았나 봐요" (The atmosphere must have been good). It works great for social media too. If a friend posts a photo of a beach, comment "재밌나 봐요!" (Looks like you are having fun!).

Do not use this for your own direct experiences. If you are eating an apple, do not say 사과가 맛있나 봐요. You know it is tasty because you are eating it! Just say 사과가 맛있어요. Do not use it for things you are 100% certain about. If someone tells you "I am a doctor," do not say 의사인가 봐요. They just told you! Use it only for guesses based on clues. Also, avoid using it for the distant future. There is a different grammar for future guesses. This one is for the "right now" or the "just happened."

Mixing up verbs and adjectives is the biggest hurdle. Remember that 맛있다 and 멋있다 act like verbs here. So use 맛있나 봐요, not 맛있는가 봐요. Another mistake is using it for yourself. If you say 나는 행복한가 봐요, people will think you are confused. It sounds like you are looking in a mirror to see if you look happy. Yes, even native speakers mess up the adjective/verb distinction sometimes. But you should try to get it right. Also, do not forget the 인가 for nouns. 의사 봐요 is wrong; it must be 의사인가 봐요.

How is this different from -(으)ㄴ/는 것 같다? That is the most common question. 것 같다 is a very broad "I think." You can use it for opinions, feelings, or guesses. 나 보다 is much more specific. It strictly requires evidence. If you have no clue, use 것 같다. If you see a wet umbrella, use 나 보다. Think of 것 같다 as a soft cloud. Think of 나 보다 as a magnifying glass. 나 보다 sounds a bit more objective because it is based on clues.